Jeremy Corbyn’s authority was challenged by both his Shadow Cabinet and his MPs last night as he faced sustained criticism over his handling of the party’s policy on Syria and terrorism.

In an extraordinary day at Westminster, the Labour leader was forced to agree a free vote on UK bombing of ISIL and had to abandon an attempt to claim that the party policy was now officially against military action.

But the most trenchant criticism came at the Parliamentary Labour Party meeting in the Commons.

Former acting leader Margaret Beckett also slated Mr Corbyn for attempting to convene a snap meeting of the ruling National Executive Committee (NEC) in an “outrageous” bid to sway the Shadow Cabinet to impose a whip against military action.

Shadow Foreign Secretary Hilary Benn, who had earlier at the Shadow Cabinet warned he was prepared to call for action against ISIL even ‘from the backbenches’, also won applause at the PLP for saying Labour’s internationalist credentials were at stake.

Mr Dromey won loud applause for attacking Mr Livingstone’s line on the BBC’s Question Time last week that the 7/7 terrorists ‘gave their lives’ for their cause in opposing Blair’s Iraq war.

Mr Dromey - husband of former acting leader Harriet Harman - said he was speaking as former assistant general secretary of the Transport and General Workers Union, one of whose members was the driver of the bus on which people were killed in Russell Square.

“How dare Ken Livingstone say what he said about those people [the terrorists] giving their lives in the 7/7 attacks? How can this man still have a role in charge of Labour’s defence review?” Mr Dromey said.

Despite long and sustained applause, Mr Corbyn didn’t reply. “He just sucked it up, he said nothing on Livingstone,” one MP said. Mr Benn, who spoke after Mr Dromey, pointedly said he agreed with everything his fellow frontbencher had said.

After the meeting, Mr Corbyn’s spokesman pointed out that Mr Livingstone had made a widely-praised speech in the wake of the 7/7 bombings.

Dame Margaret began by telling the Labour leader “This vote is not about you, Jeremy”. She also criticised an attempt by the leader’s office to call an emergency meeting of the NEC on Monday morning to discuss Syria, a move seen by some as a bid to bounce the Shadow Cabinet into backing a whip against Cameron.

“That was outrageous, outrageous,” Mrs Beckett said. “We cannot unite the party if the leader’s office is determined to divide us.”

Three Labour MPs got up to ask Mr Corbyn if there were “any circumstances” in which he would agree to commit British troops to military action. Angela Smith, shadow defence minister Kevan Jones and shadow foreign minister Pat McFadden. “He didn’t answer that either,” one MP told HuffPost UK.

Veteran MP David Winnick, who opposes the bombing in Syria, said he was worried that MPs who backed the PM were facing a ‘shakedown’ from the leftwing grassroots group Momentum, which was a ‘party within a party’. “Even though I’m with you Jeremy, there should be no threat to deselect MPs.”

Yvonne Forvargue said that the mishandling of the Syria issue had left the public thinking Labour was focused on its internal battles rather than the conflict. “This whole debate has been about us, it should be about the substance”.

And in one of the most outspoken attacks, Kevan Jones – the defence minister who recently clashed with Mr Livingstone over his mental health - accused Mr Corbyn of “subterfuge and double dealing” over the Syria vote. He said that Corbyn had been elected on a promise of straight, honest politics but after his behaviour in the past week that promise "lies in tatters."

Mr Benn told the meeting that the UN resolution had given a clear legal sanction on the grounds of self defence, while stressing that the party’s conference motion tests on a political process had been met. “We are part of a coalition of 60 countries. Some of my colleagues seem to think this would be unilateral action.”

“We are an internationalist party,” Mr Benn said, before appearing to ridicule the party leader by gesturing with his hands towards Mr Corbyn and saying “It can be argued that it is all too difficult. But that will not stand us in good stead with the British people when they look to us for leadership."

Mr Corbyn had opened the meeting by reading a summary of the Shadow Cabinet’s decision to agree a free vote, and by setting out the results of his email consultation with members. Some MPs – including Susan Elan Jones - asked about the process of the poll, pointing out £3 supporters got it but some party members didn’t and queried how 75,000 emails could be properly processed so quickly.

Ian Lavery, the leftwing MP, hit out at Lord Mandelson, who was in the room, for briefing against the leader. He also hit out at MPs who had been taking legal advice about keeping Mr Corbyn off a future leadership ballot. “Jeremy’s taken more abuse than all of us put together,” he said.

Mr Corbyn ended the meeting by asking why young people in the West, in London, Paris and Brussels, were ending up as ISIL supporters. “What is it about us, what is it about our society that makes people radicalised?” Some Labour MPs heckled “It’s not our society to blame!”

Mr Corbyn’s spokesman said afterwards that there was only a ‘minority’ of the PLP who were critical. “There was significant support for the leader,” he added.

"It was always going to be a bumpy ride when you have a leader whowas elected by a large number outside parliament, but whose support in the PLP is quite limited. There are a small number who find it hard to come to terms with that result."

Earlier, during a tense two-hour Shadow Cabinet meeting, Mr Corbyn revealed that 43% of Labour MPs had told the whips that they were minded to vote with the Government.

Mr Corbyn sought support for a move to announce that party policy was officially anti-bombing in Syria, with a suggestion that Shadow Cabinet ministers could not publicly argue against the line.

But he was met with a backlash as minister after minister said that staging a free vote and having a strong party line on bombing was contradictory. Andy Burnham said that such a move would be like throwing the frontbench ‘to the wolves’, adding he didn’t want to be part of a ‘sham Shadow Cabinet’.

Crucially, the Shadow Cabinet agreed that the party’s position adopted in a conference motion in September did not commit the Parliamentary party to oppose airstrikes. Instead, some members could argue that the tests set by the motion had been met, while the Corbyn leadership argued that they had not.

Mr Corbyn was forced to accept that while he would open the Syria debate for Labour, Mr Benn would close the debate – and both men could express their separate interpretations of Labour’s position.